1. Field of the Invention
This invention relates to thermographic measurements for the detection and measurement of thermal abnormalities of the human body, and more particularly to noncontacting measurement of subcutaneous temperature distributions for early detection of tumors.
2. Discussion of the Prior Art
X-ray techniques for the detection or measurement of structural abnormalities or diseases of the human body are being used more frequently (mammography, CT scanning, etc.). The disadvantage of these diagnostic methods is radiation exposure to the patient (B. J. Culliton, Science, vol. 193, (1976), p. 555); they are also clinically ineffective for common inflammatory processes where only temperature changes occur. Like, for example, in the most common form of arthritis (J. Edrich and C. J. Smyth, "Arthritis Inflammation Monitored by Subcutaneous Millimeter Wave Thermography", Journal of Rheumatology, vol. 5, (1978), No. 1, p. 59-67) and in the early stages of certain tumors (M. Gautherie, Y. Quenneville and Ch. Gros, in "Functional Explorations in Senology", Europ. Press, Ghent/Belgium; p. 93, 1976.
For the above applications, both infrared and plate thermography are used. These methods lead to images with good temperature and spatial resolution. Both, however, are not suited for precise measurements of subcutaneous temperature distributions because the temperature of the skin--as opposed to the subcutaneous temperature--can change significantly, i.e., several degrees and the correlation with subcutaneous processes--tumors, inflammations, etc.--is thus small. These methods therefore cannot in general be considered suitable for the early detection of breast and brain tumors (M. Moscowitz, J. Milbrath, P. Cartside, A. Zermano and D. Mandel, "Lack of Efficacy of Thermography as a Screening Tool for Minimal and Stage I Breast Cancer", New England Journal of Med., vol. 295, (1976), No. 5, p. 249-252).
Good penetration depths of several centimeters have been achieved with contacting thermography at a wavelength of about 10 cm (A. H. Barrett, P. C. Myers and N. L. Sadowsky, "Detection of Breast Cancer by Microwave Radiometry", Radio Science, vol. 12, (1977), p. 167-171). This method, however, is used in a stethoscopic fashion, and is therefore impractical; the results are also not readily reproducible because of the critical influence of miniscule air gaps. In addition, it can not localize a subcutaneous process and is restricted to integrating measurements of relatively large volumes of subcutaneous temperature distributions without precise depth determination.
Experiments to avoid these disadvantages using contactless subcutaneous temperature measurements of the human body have been reported (J. Edrich and C. J. Smyth, "Arthritis Inflammation Monitored by Subcutaneous Millimeter Wave Thermography", Journal of Rheumatology, vol. 5, (1978), No. 1, p. 59-67). Here, subcutaneously emitted thermal (black-body) electromagnetic radiation at a wavelength of 4 mm (68 GHz) was detected using a focussed arrangement which yielded a spatial resolution of slightly more than 1/3 wavelength. The power was radiometrically detected within a bandwidth of 2 GHz, integrated with a time constant of 1 to 3 seconds, and recorded. Other experiments were performed in the frequency range 66 to 71 GHz with a bandwidth of 2 GHz. The method has been used for the detection of arthritis in knee joints and breast cancer. Shorter integration times can be used for larger received powers. It is desirable to use the shortest integration time possible, with a permissible temperature fluctuation, in order to achieve short imaging times.
For the purpose of focussing the subcutaneously emitted radiation into the horn of the receiving system (radiometer), lenses made of dielectric material (plastic ) were used which had a diameter of 20 to 25 cm and a thickness of about 5 cm. For adjustment of the focal distance, two light sources with point or "V" images were attachedon each side of the lense; the space between their images on the skin indicated the depth of the subcutaneous focus. Crossing of these focussed light beams indicated the focal spot.
Satisfactory detection of deeper lying tumors, inflamed regions, or temperature abnormalities was not possible for depths of 2 to 4 cm or more although the emissivity of skin, and achievable spatial resolution, were attractive and allowed the use of conveniently sized lenses above 60 GHz. Hence, attempts were made to achieve higher detection sensitivities using larger lenses. It was soon discovered, however, that one was reaching both manufacturing as well as clinical limits as the lenses had to be made extraordinarily large. This also increased the disturbing influence of reflections and absorption.